The invention relates to a needle selection system for a circular knitting machine having, on the one hand, static, i.e., non-rotating members comprising for each needle:
a selector jack capable of a rocking movement and of a vertical movement and having an alignment butt, a selector butt and a rocking cancellation butt; PA1 an intermediate jack having a butt and capable of rocking integrally with the selector jack and capable of a vertical movement independent of the vertical movement of the selector jack; and PA1 a slider having also a butt and associated with the needle but not associated with the rocking movement of the jacks, while being capable of accompanying the intermediate jack in the upward movements thereof; and having, on the other hand, rotary members comprising in turn: PA1 operative cams; PA1 rocking cancellation cams; PA1 electronic multilevel jacquard controls, each of which comprises: an alignment cam and a plurality of selectors, located at different levels, each of which is capable of occupying a retracted position in which it does not engage the selector butts and an extended position in which there is mutual engagement between a selector and a butt, the corresponding jack being caused to rise and the selector being moved to said retracted position. PA1 if while engaged with one same operative cam, the selector jack is selected twice, the needle remains in the inoperative position; if while engaged with one same operative cam the selector jack is selected the first time and is not selected the second time, the needle is raised to the tuck position; if during such engagement the selector jack is not selected the first time and is selected the second time, the needle is raised to the operative fabric face knit position; finally if during said engagement the selector jack is not selected at all, the needle is raised to the position of needle transfer from lower cylinder to the upper cylinder.
It is an increasing requirement in the circular knitting machines of the type described to have the capacity of a large number of operative sets, i.e., feeds, thereby improving the machine performance. Each operative set is also required to provide a wide range of needle selections, each leading to a different needle position, making the machine more versatile. It is also very important for the machine to be able to run at high speeds, since there is obviously a direct relationship between the speed and the machine output. It should be recalled here that the machine speed depends on the speed of reaction of the electromagnetic means used in the needle selection.
These objectives, listed inexhaustively, are attained according to the invention by means of a selection system of the type described, wherein said selector jack and said operative cams are provided with complementary means which, when one selector jack is caused to rise, mutually engage and cause selection of the jack by rocking it; wherein one operative cam comprises a first main track adapted to receive the butt of the intermediate jack and a second main track along which there moves the butt of the slider, said second track being provided with an interrupted lower horizontal portion over which said slider butt travels when the slider has not been previously raised by a vertical upward movement of the intermediate jack, there being two electronic controls for each operative cam, such that each selector jack is capable of not being selected or of being selected one or two times during its engagement with one same operative cam.
Preferably according to the invention, the said complementary means comprise, on the one hand, an upper shoulder of the jack and, on the other hand, lower sloping surfaces of the operative cam.
Alternatively according to the invention, the following may happen:
Each electronic multilevel jacquard control may comprise a box in which there is housed generally horizontally a plurality of selectors which may slide between a retracted position and an extended position and in which each selector comprises a sheet-like member having: a head; a rear end; a slot; means housed therein urging the selector to said extended position; means for constraining said sliding movement to said extended position.
Bearing the above in mind, in a further development of the invention said head comprises: a downwardly directed portion having on the upper side thereof a surface generally having the form of an inclined plane adapted to engage the selector jack butt, thereby causing it to rise; and a prismatic cam having a generally flat vertical operative surface, adapted to be engaged by the butt of the upwardly raised selector jack, said engagement causing the selector to move from said extended position to said retracted position.
Preferably also according to the invention, said sliding movement constraining means comprise a vertical key member crossing through a rear portion of the slot of each selector.
It is known to have each box associated with an electronic and electromagnetic unit adapted selectively to retain the selectors in the retracted position thereof.
According to a further feature of the invention, each unit comprises: a single central core having central pole extensions, each of the latter being opposite the rear end of a selector; an electromagnetic coil surrounding each central pole extension; a pair of flat ceramic permanent magnets situated one on each side of the central core and in contact therewith; a pair of lateral pole extensions, each one contacting one of the permanent magnets on the opposite side thereof to the central core, said lateral pole extensions being closer to the box than the central pole extensions with the distance therebetween being greater than the width of the rear end of a selector, such that when the selector is in the retracted position, said rear end engages the corresponding central pole extension between the said lateral pole extensions, an airgap being formed between each lateral extension and the selector.